T400 dead after HW maintenance!

[thethinkguy]

I've just finished cleaning my CPU cooling system on my T400. I reassembled it back but now it won't power on:

-When I turn it on, some LED indicators turn on, but not the HDD-in-use one.

-The fan turns on, but after a second it disconnects and stops.

-The HDD seems to work as it's making sounds, but after a second it makes a really short beep and disconnects.

-Testing the mobo, I removed RAM, but I get the same behavior,

In all, it's like after a second the whole system shuts down. I don't know what could cause this, as I can't even get to the BIOS.

Any help will be appreciated!

[Cigarguy]

Check that the CPU is seated properly and the screw is turned all the way to tighten it in place.

[TankPad]

It sounds like you're not passing POST, does that sound right? I'd start by striping it down to recheck your work, making sure the heat sink is fitted right, the fan plugged in properly, the CMOS battery present, display connected etc. Does it only make a single short beep? You can look up the beep codes and see what your results relate to.

[thinkpadcollection]

Mis-seated heatsink on CPU can shut down instantly check the thermal grease made good contact with CPU die. If you have another processor, give it a try?

Cheers, thinkpadcollection

[jaspen-meyer]

Check the cpu carefully: positioned correctly, all the legs are straight, screwed in place.

Did you apply thermal grease between the cpu and the heat sink?

Also, putting the wrong sized screws in the wrong holes can cause problems.

[kfzhu1229]

Check for short circuits too. Maybe you've bent one of those metal sticking out of the palm rest into the motherboard or put the antenna in the wrong place.
I, too, have encountered random shutdowns after a T43p motherboard upgrade, thinking that the southbridge is toast and after replacing that with a spare one, same issue. Then I've learnt this the hard way - the metal part in the palm rest near the gpu area was bent down and shorted one of those surface mount parts. Even though the motherboard and the machine itself works flawlessly after bending it back, the piece of alumium metal now looks like the smoked alumium found on space grey iPhone's Apple logo lol